Shaking table tests on a cantilever retaining wall with reinforced and unreinforced backfill

Abstract

Physical modelling of cantilever retaining walls with and without backfill reinforcement was conducted on a 1g shaking table to evaluate the mitigation effect of reinforcement on system dynamics (g denotes the acceleration of gravity). The model wall has a height of 1.5 m with a scale ratio of 1/4 and retains dry sand throughout. The input motions are amplified to three levels of input peak base acceleration, 0.11g, 0.24g, and 0.39g, corresponding to minor, moderate, and major earthquakes, respectively. Investigation of the seismic response of the retaining walls focuses on acceleration and lateral displacement of the wall and backfill, dynamic earth pressures, and tensile load in the reinforcements (modeled by phosphor-bronze strips welded into a mesh). The inclusion of reinforcement has been observed to improve the integrity of the wall-soil system, mitigate vibration-related damage, and reduce the fundamental frequency of a reinforced system. Propagation of acceleration from the base to the upper portion is accompanied by time delay and nonlinear amplification. A reinforced system with a lower acceleration amplification factor than the unreinforced one indicates that reinforcement can reduce the amplification effect of input motion. Under minor and moderate earthquake loadings, reinforcement allows the inertia force and seismic earth pressure to be asynchronous and decreases the seismic earth pressure when inertia forces peak. During major earthquake loading, the wall is displaced horizontally less than the backfill, with soil pushing the wall substantially; the effect of backfill reinforcement has not been fully mobilized. The dynamic earth pressure is large at the top and diminishes toward the bottom.

摘要

目的

1. 探讨墙后填土加筋与否对悬臂式挡墙地震响应的影响规律；2. 评估填土加筋措施对改善悬臂式挡墙抗震性能的适用性。

创新点

1. 设计并制作填土加筋与填土未加筋的悬臂式挡墙模型，开展振动台模型试验的对比研究，并分析填土加筋对悬臂式挡墙地震响应的改善效果；2. 分析不同加载幅值作用下，墙-土相互作用的同步特性。

方法

1. 开展填土加筋与填土未加筋悬臂式挡墙的振动台模型试验；在模型底部分别输入加速度幅值为0.11g、0.24g及0.39g的正弦波，测试模型的加速度、位移、土压力及筋带拉力等响应量。2. 重点分析不同加速度幅值下模型的自振频率及阻尼比、加速度沿高度的放大规律、振动位移以及墙-土相互作用等规律，并对比模型动力特性及响应差异，明确悬臂式挡墙填土加筋的减震效应。

结论

1. 填土加筋对悬臂式挡墙的地震响应具有改善作用；加筋模型的加速度、位移、动土压力等响应量较未加筋模型更小。2. 基于均方根加速度的放大系数沿高度表现出显著的非线性放大效应，并随加载加速度幅值的增加呈加速增大特征。3. 悬臂式挡墙填土加筋可导致墙体所承受地震惯性力与地震土压力存在相位差，大幅降低最不利位移状态时墙体所受地震土压力；试验表明，未加筋模型中墙体惯性力与地震土压力基本同步，而填土加筋后，0.11g及0.24g加载工况下墙-土相互作用的同步性明显降低。